Description of the Prior Art:
In the ammonium sulfide process for removing hydrogen sulfide from coke oven gas, the coke oven gas containing hydrogen sulfide is introduced into the bottom of a hydrogen sulfide scrubber. Aqueous ammonia wash water is introduced into the top of the hydrogen sulfide scrubber. Cleaned coke oven gas, containing a reduced amount of hydrogen sulfide, is withdrawn from the top of the hydrogen sulfide scrubber. An aqueous ammonia liquor, containing dissolved hydrogen sulfide, is withdrawn from the bottom of the hydogen sulfide scrubber. In a typical installation, a deacidifier also is employed. The aqueous ammonia liquor, containing dissolved hydrogen sulfide, is delivered from the base of the hydrogen sulfide scrubber to the top of a deacidifier where it is countercurrently contacted with ammonia or aqueous ammonia solutions. A hydrogen sulfide gas product is recovered from the top of the deacidifier. An aqueous ammonia liquor is withdrawn from the base of the deacidifier and introduced as a portion of the aqueous ammonia wash water in the hydrogen sulfide scrubber.
A further refinement known in the art employs an ammonia scrubber for recovering ammonia gas and ammonia-rich aqueous vapors or liquids from at least a portion of the aqueous ammonia liquor which is withdrawn from the base of the deacidifier. The ammonia stripper yields ammonia gas and ammonia-rich aqueous liquids as product and also generates an aqueous liquor which is a weak ammonia aqueous solution and which may be employed at least in part as aqueous ammonia wash water in the top of the hydrogen sulfide scrubber.
It is known that the efficiency with which hydrogen sulfide is washed from coke oven gas can be considerably increased if ammonia is washed out simultaneously with hydrogen sulfide in the hydrogen sulfide scrubber. Absorption of ammonia in the hydrogen sulfide scrubber can be achieved by increasing the ammonia content of the coke oven gas; by recycling ammonia; and by simultaneously keeping the ammonia content of the scrubbing water at a low value. Heretofore the ammonia required for recycling has been obtained by withdrawing vapors from the top of an ammonia stripper or by employing coke oven gas to strip hot, deacidified recycle aqueous liquor. Corrosion of the equipment is accelerated by using the concentrated vapors from the top of the ammonia stripper and also by using hot, deacidified recycle aqueous liquor.